I generated two MP4 files - a five-second intro file, which is created by the script below, and the main video (about one minute long) is created by screen-cast-omatic, both in MP4 format. When I attempt to concatenate them using the ffmpeg -f concat -i mylist.txt -c copy output method, it produces an output file where the intro file plays fine. Then the main video plays; the audio is fine but the video is messed up where it displays garbled video on top.

Using the ffmpeg -i "concat:input1.mpg|input2.mpg|input3.mpg" -c copy output.mpg method, the output is a video which is not complete. I did not include any script output on this.

I tried using memcoder to concatenate the two videos and I get a problem there. I suspect it has to do with the codec or fps/bit rates etc, so I tweaked the script to 10 fps on both videos and here is memcoders output: